1. Field of the Invention
The invention relates to a semiconductor chip pad structure and a method for manufacturing the same, and more particularly to an arrangement with a flat area at the center of the terminal pad and a roughened area at the periphery thereof.
2. Description of the Related Art
Light-emitting diodes (LED) have a small size and a high luminous efficiency. Moreover, they are able to emit a light having different colors, thereby ensuring a various application. As a result, a lot of packaging (assembly) shapes have been created. The packaged products are generally known as lamps or SMD (surface mounting device). Apart from the appearance, another important consideration point is the quality reliability. Therefore, the wire bonding is an important step for both the lamp arrangement and the SMD-arrangement before or after the packaging process. The wire bonding is done for fitting a metal pad to the positive side of the LED chip. By application of energies such as heat, pressure and ultrasonic wave, the metal material is fitted to the surface of the pad for establishing an electric connection. In this way, the electric current tends to be delivered via the metal wire to the external lead frame. As shown in FIG. 1, one end of a metal wire 10 is connected to a terminal pad 21 of a semiconductor chip 20 by a ball bond while the other end thereof is secured to a lead frame 30 by a wedge bond.
Normally, a wire bonder is required for the ball bond. The core of the wire bonder is the bonding head (used for applying pressure). The heat energy is supplied by the mini-heater (that clamps the lead frame). However, both the pressure and the heat are provided via the bonding head. Thus, it plays an important part in the bonding quality. Any mechanic devices have their own mechanic difference and fluctuation that tend to cause an undesired wire-bonding shift for the ball bond. That is, the center of the ball bond is misaligned with the center of the pad. Accordingly, the pressure and the ultrasonic energy will be abnormally and asymmetrically delivered to the area of the light-emitting layer adjacent to the pad. In this way, it is likely to do direct harm to the light-emitting layer when the light-emitting layer (made of AlInGaP) of LED is not hard enough or when it is roughened by a special treatment. Damages like cracks or the cratering may take place and cause an adverse effect on the yield rate of the LED packaging elements as well as on the electric reliability.